1. Field of the Invention
This invention relates to new compositions useful in drilling operations wherein the drill string is stuck in the hole and cannot be readily released.
2. Description of Prior Art
During drilling operations the drill string may become stuck and cannot be raised, lowered, or rotated. There are a number of mechanisms possible which may contribute to this problem. Namely these are (1) cuttings or slough build-up in the hole, (2) an undergage hole, (3) key-seating and (4) differential pressures.
This invention relates particularly to the differential pressure problem and is intended to be a novel approach to alleviating this situation.
Differential sticking may be defined as the sticking of the drill string against a permeable formation containing less pore fluid pressure than the hydrostatic pressure exerted by the drilling fluid column and usually occurs when the drill string remains motionless for a period of time. The mechanism by which this occurs involves the drill string coming into contact with the permeable zone, remaining quiescent for a period of time sufficient for mud cake to build-up on each side of the point of contact, thus sealing the pipe against the borehole. The annular pressure exerted by the drilling fluid then holds the pipe against the borehole or the permeable zone.
Freeing of differentially stuck pipe is essentially a matter of reducing this pressure differential which exists across the pipe. One method used simply involves a reduction in fluid pressure by replacing the annular fluid with a less dense fluid allowing for less pressure differential to exist between the borehole and annulus. In some cases the borehole pressure may exceed the annular pressure which in turn allows the pipe to be blown away from the borehole.
The most commonly used method to release stuck pipe is the spotting of an oil mud in the hole opposite the stuck interval. With time, the isolated area between the drill pipe and borehole is reduced by the oil mud. Too, oil invasion into the mud cake reduces the adhesive forces and lubricates the area between the pipe and borehole resulting in less friction and quicker release. More often than not, an extensive period of time is necessary for this to occur which results in an expensive loss of rig time.
In recent years, there has been a number of proprietary formulations developed aimed at releasing differentially stuck pipe. These also seem to require a great deal of time and the success ratio is somewhat questionable.